442 DESCRIPTIONS OF SPECIES OF HELIASTER. 



The number of rays varies from 30 to 40; in eight of the specimens 

 there are from 3G to 10 rays. In the smallest specimen the free rays 

 measure about 11""" in length, in the larger specimens from 10 to 28""", 

 being generally slightly longer proportionally and more gradually taper- 

 ing than in 11. Cumingii. Most of the specimens are much compressed, 

 their thickness, however, depending upon the care taken in drying 

 them. The abactinal surface is moderately and regularly convex, the 

 median portion or disk proper being slightly elevated above the gen- 

 eral contour only in the smallest specimens. The limits of the disk 

 are, therefore, as a rule, poorly defined, tiie curvature of the abactinal 

 surface passing almost imperceptibly into that of the united portions 

 of the rays, which can generally be traced inward from the margin a 

 considerable distance, by means of the slight grooves between them, or 

 of the radiating rows of spines. In the smallest specimen the disk 

 measures about 30™"' in diameter, or slightly more than one-third the 

 total diameter; but in a larger specimen it is considerably less than 

 one-third the total diameter. The grooves between the united portions 

 of the rays are narrow and generally very shallow except directly at 

 the margin ; they are sometimes almost entirely obliterated. They 

 usually die out about half way between the margin and the disk, but 

 sometimes continue faintly to the latter. 



The spines of the abactinal surface vary somewhat in size and shape, 

 but are never relatively large, generally very small both in the young and 

 adult specimens, and usually more or less uniform in appearance in 

 each specimen, though exhibiting some variation. They are always 

 short, and either of uniform diameter throughout their length, slightly 

 tapering, or enlarging toward the summits, which, in the latter case, 

 are more or less regularly rounded, and often present a fine beaddike 

 appearance against the dark background of tlie surface. The spines 

 aie very closely placed over the entire surface. On the median portion 

 or disk they are more or less uniformly scattered, but without special 

 arrangement. On both the free and united portions of the rays, how- 

 ever, tliereis a tendency to radial arrangement, but they seldom form 

 regular rows, except along the margins of the rays. Tije lateral abac- 

 tinal rows, one on each side of each ray, are more or less regular, and 

 can generally be traced nearly or quite to the disk. In the shallow 

 grooves between them, there is usually a single row of smaller spines, 

 and three irregular rows (becoming reduced to one or two toward the 

 disk) can often be made out on the median portion of each ray. Gen- 

 erally, however, this radial arrangement of the median* spines is not 

 distinct. In one of the larger specimens, as many as seven or eight, 

 spines can be counted in the width of the broadest part of the rays. 

 The madreporic plate is circular in outline or slightly elongated, and is 

 generally placed about midway between the center and the margin of 

 the disk. 



